Illumination assemblies are used in an enormous number of different products, such as in displays for video and computer equipment, lighting equipment, etc. A typical light source in an illumination assembly, such as a light emitting diode (LED), often does not have an optimal radiation pattern for the application. For example, most of the illumination from an LED die may be directed primarily from the top and sides of the die, resulting in wasted light from the sides and a spotlight effect from the top of the die. A display using LED dies without other features to condition the radiation pattern from the LED dies might appear both dim and uneven or spotty.
Conventional illumination assemblies may include an encapsulant over the LED die that has a highly diffusive material dispersed throughout the encapsulant. One example of an encapsulant with a highly diffusive material is an epoxy with many fine borosilicate particles spread throughout the epoxy. The diffusive encapsulant does provide several benefits, such as physical protection of the LED die and random scattering of the light rays from the LED die as they pass through the encapsulant and hit the particles. The resulting light from the illumination assembly thus has a more diffuse than specular character. Unfortunately, diffusive encapsulants also have several disadvantages. As the light passes through the diffusive encapsulant and is scattered, flux losses in the light may be high due to the three dimensional, volumetric scattering of light bouncing back and forth within the encapsulant. The use of a diffusive encapsulant over the light source may also lead to physical weakness or failure if another encapsulant is used over the top of the diffusive encapsulant. For example, if the diffusive encapsulant is placed over an LED die and another structural non-diffusive encapsulant is placed over that in the illumination assembly, the two encapsulants may have coefficients of thermal expansion. As the illumination heats up under use, the different encapsulants expand at different rates, causing failure of components at boundaries between the encapsulants. If a wire bond for the LED die passes through the boundary between the two encapsulants, it is susceptible to breakage due to the different coefficients of thermal expansion. Finally, the radiation pattern generated as light passes through a diffusive encapsulant is very difficult to sculpt or direct.